After this discovery, I took to #erlang-lisp and tried to figure out why.
Discussing the issue with @rvirding for a few minutes, we decided adding ++*
and having patterns like (++* "prefix" suffix) expand to nested cons-es was
a solid approach.

N.B. In v0.10.1, exp_append/1 had the following clause, commented out.

Rather than take the overly complicated approach of counting and limiting the
number of expanded cons-es and bottoming out to a call to erlang:++, we
decided to keep it simple and just let ++* patterns do their own thing.